1. Field of the Invention
The present invention relates to an optical organism measuring apparatus, which is adapted to obtain vital information by applying light such as visible radiation or near infrared radiation to an organism and measuring the light transmitted through or reflected (including scattered light) by the same.
2. Description of the Background Art
Some of optical measuring apparatuses are provided with optical paths which are formed by optical fibers. For example, a laser tissue blood flow meter, which applies laser light to an organism through a single-core fiber and receives the reflected light by an optical fiber for calculating the tissue blood flow volume, has already been put on the market. The light reflected by the organism is obtained from a portion which is in close proximity to an end exposed to the light.
U.S. Pat. Nos. 4,223,680 and 4,281,645 disclose an apparatus which applies light emitted from a light source to a vital tissue through an optical fiber bundle and receives the light reflected by the vital tissue through a light receiving optical fiber bundle which is arranged on the central axis of the said optical fiber bundle for application of light or another portion for guiding the reflected light to a detector.
There has also been provided an apparatus called a pulse oxymeter, which is adapted to directly fix an LED to an organism and receive light transmitted through a fingertip or the like by a photodiode, thereby measuring oxygen saturation in arterial blood.
Light which is applied for measuring information in an organism is extremely attenuated due to scattering or absorption caused in vivo. Even if narrow light is applied, the same is scattered in the organism and spread over a wide area toward all directions of a 2.pi. space (half plane) in the detecting side. Therefore, both light transmission and receiving sides must be devised in order to improve sensitivity.
The aforementioned organism measuring apparatus for calculating the tissue blood flow volume has strong intensity for obtaining vital information from a portion in close proximity to an end which is exposed to light by a reflection method, and no problem is caused in particular in a measuring system employing an optical fiber. In order to obtain information from a deep portion in the organism, however, optical fiber bundles which are formed by numbers of optical fibers are generally employed in both light transmission and receiving sides due to strong scattering and absorption caused in vivo. Also in this case, the optical fiber bundle employed in the light receiving side must be increased in thickness if a light transmission length in vivo is about several cm, in order to improve detection sensitivity for light which is transmitted through or reflected by the organism. When the optical fiber bundle is thus increased in diameter, however, it is difficult to stably fix the same to the organism due to its own weight.
Even if the light is received by an optical fiber bundle having a large diameter, there remains a problem of fiber loss which is varied with the charging rate of the optical fibers contained in the optical fiber bundle, the core ratios in the respective optical fibers, the propagation rates of the transmitted or reflected light entering the cores, and the like.
The light receiving side is preferably pressed in close contact against the organism, in order to omnidirectionally catch the transmitted or scattered light over a wide area. In this point, the quantity of light is reduced in relation to a handleable optical fiber bundle having a small diameter, and only light energy within a propagation angle of a core portion of the optical fiber bundle is used.
As to the light transmission side, on the other hand, it is advantageous that a high output can be obtained with monochromatic light. However, in a measuring system such as a pulse oxymeter employing an LED, for example, the as-obtained light output is restricted. Such a pulse oxymeter can merely measure light which is transmitted through a fingerpoint at the most, due to a small light output of the LED. Further, measuring accuracy is deteriorated since the bandwidth of the LED is too large.